I would like some help with this scenario.

Elizabeth and Jessica are distant cousins. They enjoy each other's company and have a very good relationship. Jessica's husband, Fred, is a Carpenter/Mason with several years' experience on the job.

It so happens that Elizabeth was looking to renovate her downstairs toilet and bath and required the services of a Carpenter/Mason. Knowing that Fred can do that type of work, Elizabeth got his number from Jessica and Fred and Elizabeth reached an agreement in accordance with the following terms:

1. Fred will break down and reconstruct the toilet and bath;

2. This job will take 2 weeks to complete, commencing from 18th January 2021 and ending on the 1st of February 2021;

3. All building supplies will be provided by Elizabeth who will retain all receipts;

4. Elizabeth will pay to Fred the total sum of $150,000.00 (one hundred and fifty thousand dollars), half of which to be pay on or before the 25th of January 2021; and

5. Should any additional work be done, Fred and Elizabeth must agree to the terms in writing.

Fred commenced working on the toilet and bath, and soon realised that there would be additional work to be done. He indicated this to Elizabeth, who told that he should do what needs to be done to get the work done.

The additional problems were that Fred found the beams above the toilet and bathroom needed to be replaced before he could start building. There was also the issue that the septic system appeared to be clogged up and needed to be pumped before any other work can commence.

These problems resulted in delay. Instead of 2 weeks, it took Fred 4 weeks to complete the job that he was employed for.

Elizabeth, though satisfied with the job done, is unwilling to pay Fred any additional sums of money for the extra work done by him as "it was not in writing".

Discuss the issues that arise from the above scenario.